Salt bath furnace



Feb. 1,1, 1947. A, F, HOLDEN .2,415,493

SALT B ATH FURNACE Filed Nov. 27, 1944 INVENTOR s 14g@ vas FFO/den@4a-1.7L ATTORNEY Patented Feb. il, A1947 unirse STATES PATENT oli-'Fica2,415,493 sAL'r BATH FUnNacs Artemas F. Holden, New Haven, Conn.

Application November 27, 1944, Serial No. 565,291

8 Claims. l

The present invention relates to improvements in salt bath furnaces andmore especially to a salt bath furnace for heat treatment of metalswherein the saltbath is heated by electrodes immersed in the bath.

The present invention has to do primarily with the shape of the pot forcontaining the salt bath, which shape is constructed in such manner thatthe electrodes for heating the salt bath may be located outside of theworkin-g area of the pot. This construction provides a maximum area inwhich metal parts may be heat treated without the parts coming too closeto the'heating electrodes.

TIhe shape of the pot according to the present invention has to do moreespecially with the plan View thereof rather than with other portions ofthe pot.

Other and further advantages of the present invention will in part beobvious and will in part be pointed out hereinafter in the specificationby reference to the accompanying drawing forming a part thereof.

`It is to be understood that the disclosure herewith presented is to beconsidered illustrative and is not to be construed in a limiting sense.

Fig. 1 illustrates a horizontal section comprising aplan view of anelectrical furnace in accordance with the present invention;

Fig- 2 illustrates a horizontal section showing a plan view of aslightly different form of electrical furnace from that illustrated inFig. l; and

Fig. 3 illustrates a horizontal sectional view in plan of an electricalfurnace in accordance with the present invention and differing slightlyfrom that illustrated in Figs. 1 and 2.

In melted salt baths for'the heat treating of metals, which baths areheated by electrodes vimmersed in the bath, it is desirable that thereshall be an unobstructed zone in which the metal parts to be heattreated may be immersed in the bath, and to this end, the presentinvention (referring to Fig. l) comprises a pot A which, when viewed inplan on a horizontal section, comprises an end wall I, side walls 2 and4, and end walls 5 and 6,

which meet at the angle of 90, whereby the area from an imaginary planeindicated by the dot'- ted line 1, and completed by the end walls 5 and6, comprises a right angle triangular area. Electrodes 8, 9 and I0 arelocated within this triangular area and preferably the centers of theelectrodes 8, 9 and I0 are at the apices of a 60 triangle II. It will beobserved that the area of the pot bounded by the end wall l, the sidewalls 2 and 3, and the dotted line 1, is a rectangular 1 area which isfree from obstruction since the electrodes are located within thetriangular area previously specified as comprising the area bounded bythe end walls 5, 6 and the dotted line 1.

In this construction the liquid salts within the pot circulate byconvection currents in such manner that the entire bath is retained atsubstantially uniform heat, so that the range of heat in variousportions of the bath is not suillcient to impair proper operation of thebath for heat treatment of metal parts.

. Fig. 2 illustrates a pot B of a construction similar to thatillustrated in Fig, l with the exception that the side Walls I2 and I4meet at a 60 angle so that the area between the dotted line 1 and theside walls I2 and I4 comprises a 60 triangular area. Here again theelectrodes 8, 9 and I0 are preferably arranged on the apices of the 60triangle so that the distances between all of these electrodes are equaland the distances from the electrodes to the end side Walls of the ltends beneath the bottoms of the pots and around Y on the apices of a 60triangle in an area at thev end of the pot which is substantiallytriangular and is outside of the cylindrical unobstructed working area.The curved dotted line I9 lwhen joined with the side walls I1 and I8which continue into the partially cylindrical surface I5 subscribes anarea which ivs practically cylindrical .Y

whereby this zone is capable of use without interference of anyelectrodes.

In accordance with the present invention the pots A, B, and C, whilepreferably ceramic, may -be formed of metal or other I'material suitablefor the purpose of holding melted salts comprising a liquid salt bathfor heat treatment of metals. These pots A, B and C are surrounded bysuitable heat insulating material 20 that may be held within av steel orother suitable material,

'shell 2| so as to properly sustain the pot and insulate the sameagainst heat loss. It-is to be understood the heat insulating material20 ex the several sides thereof, the pots being open at the top as iscommon in the art.

While the present invention is designed more i especially for hightemperatures from 1700 to 2350*? it has also been found to operatesatisfactorily on temperatures below 1700".

The electrodes, which are of the usualltype,

' preferably are located at the apices of a 60 tri' angle. where threephase alternating current is used to supply the energy for heating thebath. These electrodes comprise rods of suitable material which areimmersed in the salt in the bath.

' asians 5. An electrical furnace of the electrode type for heating saltbaths for the treatment o! metal load and to properly heat the salt bathin the pot with this type of electrical current.

While the construction illustrated in Fig. .2, having the 60 end walls,is satisfactory for smailparts, comprising a ceramic pot withsubstantially vertical side walls and having a portion of s aid sidewalls extended outwardly from the main portion of the pot to provide asubstantially triangular recess in horizontal cross-section forming aheating zone, three equispaced electrodes mounted in said heating zonewhereby the reer type baths, the construction illustrated in Fig.

1, having the 90 end walls, seems slightly better adapted for a largersize pot, and the construction shown in Fig. 3 may be used for eitherthe larger sizes or the smaller sizes. Furnaces in accordance with thepresent` invention have pots with substantially vertical walls and havebeen constructed and operated with the useable area varying from 280square inches to about 45 square inches.

The electric energy supplied through the electrodes lhas varied from 125kva. vfor the larger pots to 30 kva. for the smaller pots. A 7

The present invention has beeniound to increase the eifective operatingfree area of the furnace without substantially detracting from the`eillclency thereof or without substantially increasing heat losses.What I claim is:

1..In'an electrical furnace for heating salt baths for the heattreatment of metal, the commainder of said pot comprises an unobstructeworking zone.

c 6. An electrical furnace of the resistance elec trode type for heatingsalts lto comprise a bathV for the heat treatment of metal parts, saidpot having substantially vertical side walls with a substantiallytriangular area in horizontal crosssection extending outwardly from themain portion of the pot and thereby providingthe remainder of the pot asan' unobstructed working zone in which said metal parts may be immersedin the bath, and three equispaced electrodes arranged in triangularrelation to each other withy in the substantially triangular area toheat said bination of a pot for containing the salt bath and wherein aportion of a side wall of said .pot extends loutwardly to forma zone 4inwhich electrodes may be located to provide a portion of said pot capableof receiving metal parts to be heat treated, and three electrodeslocated within said zone with' each electrode being equidistant from theother two electrodes to obtain a balanced three phase electrical loadbetween electrodes.

within said recess whereby there is established a working zone free ofelectrodes and wherein said electrodes being equidistant one fromanother provides a balanced three phase electrical load.

' 3. An electrically heated furnace adapted for heat treatment of metalparts in a liquid salt bath, said furnace comprising a, pot adapted tohold the salt bath and having an outwardly extended portion inthe sidewall of said pot to provide aheating zone, and three electrodes mountedwithin said heating zone on the apices of a 60 triangle, the remainderof said pot comprising bath.

7. An electrical furnace for heating salts for.

the heat treatment of metal parts, said furnace comprising a pot havinga heating zone and a working zone, said heating zone being created byextending outwardly a portion of the walls of said pot to intersect atan angle not in substantial excess of 90 or substantially less than 60to provide a recess of substantially triangular arca in horizontal crasssection, and three electrodes in triangular relation symmetricallypositioned within said recess whereby there is established a workingzone free of electrodes and wherein said electrodes provide asubstantially balanced three-phase electrical load.

8. An electrical furnace forheating salts for the heat treatment -ofmetal parts, said furnace comprising a pot having a heating zone and aworking zone, said heating zone being created by extending outwardly aportion of the walls of said pot to intersect at anangle ofsubstantially 60 to provide a recess df substantially triangular area inhorizontal cross section, and three electrodes in triangular relationsymmetrically positioned within said recess whereby there is es- I..tablished a working zone free of electrodes and a working zonesubstantially free from any obstruction and with the walls of said potbeing substantially vertical..

4. An electrical furnace4 ofthe electrode type f for heating salt bathsfor the treatment of metal parts, comprising a, ceramic pot withsubstanl tially vertical side walls and having a portion of said sidewalls extended outwardly from the main portion of the pot to provide arecess forming a heating zone, electrodes mounted onthe apices of a 60triangle in said heating zone whereby the .wherein said electrodesprovide a substantially REFERENCES crrnn The following references are ofrecord ln the ille of this patent:

UNITED STATES PATENTS Number Name y Date s 1,782,482 Seifert et al. 1.Nov. 25, 1930 1,811,754 Hultgren Junev 23, 1931 2,234,476 Jessop Mar.11, 1941V 1,373,615 Jacobs Apr. 5, '1921 1,792,674 Bellis Feb. 17, v19311,864,885 Bellis June 28, 193,2 1,985,623 Ross Dec. 25, 1934 V2,145,677Adam, Jr. Jan. 31, 1939 2,336,412 Messinger Dec. 7, 1943 2,089,690.Cornelius Aug. 10, 193'? .FOREIGN PATENTS Number Country x Date 422,868British Jan. 21, 1935 215,009 Swiss Aug. 16, 1941

